This invention relates generally to a mechanism for conveying and de-aerating a finely powdered product, and particularly to a vibrating hopper having an inverted vented pressure cone with a central compressing auger, used in combination with an infeed auger and a transverse conveying auger which similarly de-aerate and compress the product.
Vibrational movement has been utilized for many material handling operations, including conveying articles as shown in U.S. Pat. No. 4,398,612; reorienting or disengaging irregularly shaped objects as shown in U.S. Pat. No. 4,462,508; discharging or dispensing particulate matter as shown in U.S. Pat. No. 4,530,431; and sifting or separating products as shown in U.S. Pat. No. 3,528,386. Vibrational movement is also known to de-aerate and settle both particulate and granular matter, the degree of de-aeration and settling depending in varying proportions on the intensity and direction of the vibration, the duration of the vibration, and the physical and chemical properties of particulate or granular matter itself. Some products may also be de-aerated by compression, such as in a screw feed auger.
Various rotary feed auger systems for dispensing particulate matter into containers are known. U.S. Pat. No. 4,582,097 to Ixxi discloses a device for top filling containers on a conveyor belt, the hopper having a vertically disposed central auger wherein successive auger revolution rates are determined by measuring the weight of the product previously delivered to a container and computing the ratio of auger revolutions to product weight, and then adjusting the auger revolution rate and time according to that ratio to deliver the desired weight of product to the subsequent container. The Ixxi '097 patent also discloses measuring the number of auger revolutions after the auger is disengaged until it brakes completely to calculate a wind-down number which is subtracted from the number of revolutions needed to obtain a desired fill weight. The accuracy of such a system is limited by the degree of consistency in the density of the product which can be achieved and maintained as the auger is repeatedly engaged and disengaged. While such a system can be useful in two-stage bulk and top fill applications where the initial bulk filling by weight requires only moderate precision, it has not proven suitable for two stage filling where product is topped directly from the dispensing spout (such as in a vertical bottom fill auger) or where high precision is required.
Vertical rotary feed augers of the type described above have relatively short compression paths, thereby placing an upper limit on the maximum density that can be achieved with certain powered products. While some products will become fluid or lose their inherent physical properties at too great a compression, or will bind and seize within an auger tube, other products are capable of withstanding tremendous compression and in some cases will flow better under these conditions. In these cases, where optimal density is limited by the physical properties and tolerances of the particular material, the length of the compression path through the auger tube may be too short, or the necessary revolution rate of the auger too slow, to achieve optimal compression. Conversely, increasing the auger speed may then limit the accuracy of the device, particularly due to the agitation created when the auger is started.
U.S. Pat. No. 4,629,328 to Revelt discloses a gravity blending apparatus having an inverted cone within a stationary hopper, the cone being vented to a position above the product level within the hopper. Other vented and unvented pressure cones within material handling hoppers were previously known, representative examples being shown in U.S. Pat. Nos. 4,553,849, and 4,473,300 to Goins; 4,285,602 to Hagerty; and 3,936,037 to Leonard. These inverted pressure cones permit accelerated gravity blending and promote uniformity in product density, with the vented cones assisting in the release of air backpressure to enhance the settling of the product as it accumulates in the bottom of the hopper and flows through the discharge spout, but they similarly would interfere with the use of a vertical rotary feed auger. Used alone or in combination with the rotary feed augers described above, the gravity blending devices having inverted pressure cones as shown above will not permit continuous compression of the product to a uniform and controllable density.